"Dave’s Sister: Dave. I love you, and I’m trying to help you. I really care about you. And these friends that you hang out with . . . they’re not friends. A friend is a person who is honest and frank with you, not these so-called buddies you’ve got that encourage you to go and buy booze for any old party.

Dave: You just know them like I don’t. I mean . . .

Dave’s Sister: I know them well enough. Come on. Wake up. These guys are dragging you down.

Dave: I’ve had enough."

Could you explain the meaning of "You just know them like I don't" and "I've had enough" in this dialogue?